Tutorial

So, you want to develop an application with Python and weppy, huh? We should
start with an example.

We will create a simple microblog application, using weppy and a database.
SQLite comes out of the box with Python, so you won't need to download anything
other than weppy.

If you want the full source code in advance, check out the example
source.

Bloggy: a micro blog

We will call our blogging application bloggy and, basically, we want it to do
the following things:

let users sign up and then sign in and out with their own credentials

let only an admin user add new posts (consisting of a title and a text body)

show all posts' titles in reverse order (newest on top) to everyone on the index page

show the entire post on a specific page and allow registered users to comment

– hem, dude.. seems like quite a lot of stuff for a "micro" blogging application
– relax! you'll see that every feature will be short work with weppy

Application structure

Let's start from the basis, and create this directory structure:

/bloggy
/static
/templates

The bloggy folder won't be a python package. It's just somewhere to drop our
files. In the next steps, we will build our application with a single python file,
since it's small. The files inside the static folder will be available to
clients via HTTP. This is the place where you should put the CSS and JavaScript
files. The templates you're gonna create later in this tutorial will go in the
templates directory instead.

Now you can test your application simply issuing the following command (inside
the bloggy folder):

> weppy --app bloggy.py run

and you will see a message telling you that the server has started, along with
the address at which you can access it.

When you head over to the server in your browser, you will get a 404 Page Not
Found error because we don’t have any exposed function yet. However, we will
attend to that a little later on. First, we should create the database for the
application.

Database schema

The first step in coding our application is to create the database schema.
In bloggy, we need at least 4 tables:

The users table

A users' groups/permission table (to allow only the admin user to write posts)

The posts table

The comments table

Now, this might sounds complicated, but it's actually not. In fact, we can skip
all the schema about users since weppy includes an authorization module that
creates the tables we need automatically.

So, how will we build our schema? We will use the default AuthUser class for
the users table and authorization system, and the Model class for the other
tables:

That's it. You can see we defined some relations between our models,
which will be a relationships between the tables, so we have these conditions:

a post always have one author, and an author can have many posts

a comment always have one author and always refers to one post,
and a post can have many comments

Moreover, we have set some default values (like the dates and the authors) and we have hidden some fields in forms to the users using the fields_rw attribute: it would be pointless to have an user field if the user could set this value to whatever he or she wanted. Accordingly, we're telling to weppy to auto-set those values to the right ones.

We've also added some validation, so we can prevent users from sending empty
posts or comments.

Note: as you can see we imported the now method for the deault values of the datetime fields. This method can be quite useful since it will return alternatively the time of the request or the system current time, depending on the context. You can safely use it in your application whenever you need the actual time and you have no ensurance a request context is available.

Initialize the database and the auth module

We've defined our schema, so now it's time to add the database and the authorization system to bloggy. First, let's configure the auth module a bit:

These options allow us to use a single template file for everything regarding the auth, and, since we're writing just a simple application, prevent it to use a mailer system for validating our users. The hmac_key will be used to crypt the passwords into our database.

Now, we can write down the code to use the database and the auth. Just the next few lines are enough:

The code is quite self-explanatory: it will add an user who can sign in with the walter@massivedynamics.com email and pocketuniverse password, then it creates an admin group and adds the Walter user to this group.

Also, notice that we added the @app.command decorator, which allow us to run our setup function using the weppy command shell:

> weppy --app bloggy.py setup

Now that the backend is ready, we can prepare to write and expose our functions.

Exposing routes

Before we can start writing the functions that will handle the clients' requests, we need to add the database and authorization pipes to our application, so that we can use them with our functions following the request flow.

Moreover, to use the authorization module, we need to add a session manager to the application's pipeline, too. In this tutorial, cookie support for session will be enough, and we will use Walternate as a secret key for encrypting cookies.

Since this list will only show up the posts' titles, we also write a function
to retrieve details for a single post:

fromweppyimportabort@app.route("/post/<int:pid>")defone(pid):def_validate_comment(form):# manually set post id in comment formform.params.post=pid# get post and return 404 if doesn't existpost=Post.get(pid)ifnotpost:abort(404)# get comments and create a formcomments=post.comments(orderby=~Comment.date)form=Comment.form(onvalidation=_validate_comment)ifform.accepted:redirect(url('one',pid))returnlocals()

As you can see, the one function will show the post text, the comments users
have written about it, and a form that allows users to add new comments.

We also need to expose a function to write posts, and it will be available only
to users in the "admin" group, thanks to the requires decorator:

If a user tries to open the "/new" address without being a member of the admin group, weppy will redirect them to the index page.

Finally, we should expose the auth module routes, in order to let users sign up and sign in on bloggy. Since the auth module provides a convenient application module, we can just initialize it:

auth_routes=auth.module(__name__)

and the auth module will expose everything for us.

Now that we have all the main code of our application ready to work, we need the templates to render the content to the clients.

The templates

We should create a template for every function we exposed. However, since the
weppy templating system supports blocks and nesting, and we don't really want
to repeat ourselves when writing code, we will start with a main layout file
under templates/layout.html, and we will extend it with the functions' templates:

The remaining template for our blogging app is the one for the posts creation, that will show the form. It's the simplest template since we can just write down in new_post.html these lines:

{{extend 'layout.html'}}
<h1>Create a new post</h1>
{{=form}}

We still need a template for the auth module. We should create an auth folder inside the templates one, and, since we configured the module to use just one template, we can write down these lines in the auth.html file inside it:

As you can see, the only difference from the template we wrote before to create new posts are the lines to flash messages from the auth module. This will be quite handy to display errors or notify the user.

Some styling

Now that everything works, it's time to add some style to bloggy.
We just create a style.css file inside static folder and write down
something like this:

Go ahead

You've completed the tutorial, with a new blogging application
written in very few lines, and simple ones at that. You should be more confident
with the weppy workflow and its syntax, so feel free to start writing your own applications!

To explore all the features of weppy, and better understand what you've done in
this tutorial, you should read the complete documentation,
and try to expand this simple application with more features,
so that it can better meet your needs.